Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder.
Further, engines have been proposed using more than one type of fuel injection. For example, the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. are one example. Specifically, the Heywood et al. papers describes directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle. The ethanol provides increased charge cooling due to its increased heat capacity compared with gasoline, thereby reducing knock limits on boosting and/or compression ratio. In this way, improved engine fuel economy may be achieved.
However, the inventors herein have recognized several issues with such an approach. Specifically, utilizing multiple injectors for a single cylinder to delivery two fuel types can increase cost. Also, direct fuel injection may further increase system cost, and when using an associated high-pressure fuel pump, can reduce fuel economy due to increased parasitic losses. Furthermore, it may be difficult to package both a port and a direct injector in some engine configurations, thus resulting in compromised valve sizes, valve angle, intake port shape, injector targeting, or other engine design parameters.
Thus, in one approach, a system for an engine is provided. The system comprises: an injector coupled to the engine and configured to inject fuel to a cylinder of the engine; a first reservoir holding a first fluid containing at least a fraction of gasoline; a second reservoir holding a second fluid containing at least a fraction of ethanol; a mixing device having an inlet portion coupled to both said first and second reservoir, said mixing device further having an outlet portion coupled to said injector.
In this way, it is possible to provide both the first and second fluid to the engine cylinder in varying ratios for varying operating conditions. This can provide improved overall engine efficiency, leveraging one fluid against the other. And, this operation can be achieved without requiring multiple fuel injectors for each cylinder (although in some examples, multiple injectors may still be utilized, even with the mixing device, if desired).